The barium catalyst refers to an elemental barium or barium compound which has a catalytic function. Barium is a soft, alkaline earth metal with a silvery white luster that belongs to group IIA elements of the periodic table. Because it is in the alkaline earth metal position in the periodic table, it is very active in nature and is the most active in alkaline earth metals. It can be seen from the potential and ionization energy that the barium has a strong reducibility. Even so, it is one of the most active metals in acidic solutions, second only to lithium, strontium, rubidium and potassium. So in nature, no single barium has been found. The most common minerals in nature are barite (barium sulphate) and toxic heavy stones (barium carbonate). The barium catalyst also seldom refers to a single barium element, but an oxide or hydroxide of barium.
Figure 1. Barium oxide as a catalyst
Figure 2. Barium hydroxide as a catalyst
Due to the excellent performance of the barium catalyst, it has been widely used in industrial production and environmental protection.
- Industrial production: Ethoxylation to produce nonionic surfactants is of great industrial importance because it strongly reduces the number of unreacted substrates and oligomers. Many alkaline earth metal catalysts are useful for promoting narrow range ethoxylation in the production of nonionic surfactants, with the most used barium catalysts. The barium oxide or the hydroxide can be used as a catalyst for the ethoxylation reaction, but the most widely used industrially is barium oxide. The transesterification reaction is a method for preparing a renewable clean energy source. Catalysts for the preparation of biodiesel by transesterification are mainly classified into the following types: homogeneous acids, heterogeneous acids, homogeneous bases, heterogeneous bases, and lipases. As a heterogeneous alkali catalyst, barium hydroxide has been successfully used in transesterification to prepare biodiesel because of its advantages of easy separation from products, simple reaction steps, low environmental pollution, and high purity of reaction products.
- Environmental protection: Photocatalytic water pollution control is an effective technology to solve environmental pollution problems. Nanostructured materials can provide more surface active sites, and the photogenerated electron-hole pairs are less likely to recombine in their bulk phase, which can greatly improve their photocatalytic efficiency. Barium titanate has excellent ferroelectricity, high dielectric constant and optical properties. Although there is a limitation of the wide band gap of barium titanate, a structural transformation occurs at the Curie temperature (120 ℃), and the internal spontaneous polarization field can effectively promote the separation of photogenerated charges and accelerate the catalytic efficiency. Different morphologies of barium titanate nanocrystals have different physicochemical properties, such as dodecahedral barium titanate nanocrystals with smaller particle size and larger surface activity, while cubic barium titanate nanocrystals have larger particle size and smaller surface activity, but both have photocatalytic properties, can be used as a catalyst to catalyze the degradation of contaminants. Degradation of plastics, especially polystyrene (PS), not only solves environmental pollution problems, but also becomes an important method for obtaining energy and chemical raw materials. When the polystyrene is melted and decomposed by high temperature, the viscosity is very large, resulting in uneven temperature distribution and local overheating. It is easy to cause secondary reaction and lead to carbonation, and at the same time reduces the yield of styrene monomer. The use of barium catalysts for the degradation of polystyrene reduces the activation energy of styrene degradation, thereby reducing the degradation temperature of styrene and increasing the yield of styrene monomer. In the industrial degradation of polystyrene, a barium oxide catalyst is often used.
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